Process of making fibers for reinforcing matrix materials

ABSTRACT

Preferred methods for manufacturing such fibers involve subjecting synthetic polymer fibers to compressive forces sufficient to achieve flattening and surface micro-diastrophism without substantially shredding and abrading the fibers.

This application is a divisional of U.S. Ser. No. 09/640,569 filed Aug.16, 2000 now U.S. Pat. No. 6,265,056, which is a divisional of U.S. Ser.No. 09/416,012 filed Oct. 8, 1999, and now U.S. Pat. No. 6,197,423.

FIELD OF THE INVENTION

This invention relates to synthetic polymer fibers useful forreinforcing matrix materials, and more particularly to fibers havingmicro-mechanically-deformed morphologies useful for enhanced performancein matrix materials such as asphalt, rubber, plastic, or in such matrixmaterials such as ready-mix concrete, shotcrete, bituminous concrete,gypsum compositions, or other hydratable cementitious compositions; tomatrix compositions containing such fibers; and to methods for treatingfibers and for modifying matrix materials.

BACKGROUND OF THE INVENTION

Although the fibers of the present invention are believed suitable forreinforcing a number of matrix materials, such as adhesives, asphalt,composites, plastic, rubber, etc. and structures made therefrom, theyare primarily intended for reinforcing hydratable cementitiouscompositions such as ready-mix concrete, precast concrete, masonryconcrete, shotcrete, bituminous concrete, gypsum compositions, gypsum-and/or Portland cement-based fireproofing compositions, and otherhydratable cementitious compositions. A major purpose of the fibers ofthe present invention is reinforcing concrete (e.g., ready-mix,shotcrete, etc.) and structures made from these. The task of reinforcingmatrix materials such as these poses one of the greatest challenge fordesigners of reinforcing fibers.

Concrete is made using a hydratable cement binder, a fine aggregate(e.g., sand), and a coarse aggregate (e.g., small stones, gravel), andis consequently a brittle material. If a concrete structure is subjectedto stresses that exceed its maximum tensile strength, then cracks can beinitiated and propagated in the concrete. The ability of a concretestructure to resist crack initiation and crack propagation can beunderstood with reference to the “strength” and “fracture toughness” ofthe fibers.

Fiber “strength” relates to the ability of a cement or concretestructure to resist crack initiation. In other words, fiber strength isproportional to the maximum load sustainable by the structure withoutcracking, and is a measurement of the minimum load or stress (e.g., the“critical stress intensity factor”) required to initiate cracking inthat structure.

On the other hand, “fracture toughness” relates to the specific“fracture energy” of a cement or concrete structure. This concept refersto the ability of the structure to resist propagation—or widening—of anexisting crack in the structure. This toughness property is proportionalto the energy required to propagate or widen the crack (or cracks). Thisproperty can be determined by simultaneously measuring the load requiredto deform or “deflect” a fiber-containing concrete (FRC) sample at anopened crack and also measuring the amount or extent of deflection. Thefracture toughness is therefore determined by dividing the area under aload deflection curve (generated from plotting the load againstdeflection of the FRC specimen) by its cross-sectional area.

In the cement and concrete arts, fibers have been designed to increasethe strength and fracture toughness in reinforcing fibers. Numerousfiber materials can be used for these purposes, such as steel, syntheticpolymers (e.g., polyolefins), carbon, nylon, aramid, and glass. The useof steel fibers for reinforcing concrete structures remains popular dueto the inherent strength of the material. However, one of the concernsin steel fiber product design is to increase their “pull out” resistancebecause this increases the ability of the fiber to defeat crackpropagation. In this connection, U.S. Pat. No. 3,953,953 of Marsdendisclosed fibers having “J”-shaped ends for resisting pull-out fromconcrete. However, stiff fibers having physical deformities may causeentanglement problems that render the fibers difficult to handle and todisperse uniformly within a wet concrete mix. More recent designs,involving the use of “crimped” or “wave-like” polymer fibers, may havesimilar complications, depending on the stiffness of the fiber materialemployed.

U.S. Pat. No. 4,414,030 of Restrepo disclosed the use ofmicrofibrillated polyolefin filaments that are oriented in all spatialdirections by subjecting fibrillated ribbons to air, thereby spreadingout the separate fibers, and then feeding these separated fibers into amortar mixing machine fitted with a high-speed propeller to blend themortar components and fibrous materials together. The mechanicalshredding action which takes place in the mixing operation causes theribbons to become further fibrillated, such that the ribbon fibrils arebroken apart into individual filaments having a branched structure withmicrofibrils outwardly projecting along their length. The projectedmicrofibrils are somewhat curled in shape and perform as anchoringelements or “hooks” within the cement hardened matrix. It is generallybelieved that side branches or “hooks” can act to resist fiberdislodgment or pull-out from the cement matrix and present enlargedsurface area for anchoring within concrete. The physical branched fiberstructure would appear to create entanglement problems that would renderhandling and dispersion within a wet concrete mix somewhat difficult toachieve.

U.S. Pat. No. 5,753,368 of Berke et al. taught fibers having a glycolether-based coating for enhancing bond strength of the fibers withinconcrete. Berke et al. further taught that the fibers could be bundledusing mechanical or chemical means, and that the fibers could beintroduced into a cement composition using packaging technology tofacilitate mixing and dispersion within concrete. This technology may beapplied to varieties of fibers and shapes to enhance pull out resistancewhile facilitating uniform dispersion within the concrete mix.

U.S. Pat. No. 5,298,071 of Vondran discussed the problem of achieving auniform dispersal of fibers within a wet cement mix. Vondran noted thatfibers were typically added to the mixer with the cement, sand,aggregate, other admixtures, and water. His approach was to add fiberprecursors (e.g., steel fibers and polyolefin in the form of extrudedmonofilament or fibrillated sheet fiber) and cement clinker to a ballmill grinder and to obtain a hydratable mixture comprising intergroundfibers in a dry hydratable cement powder that could then be used formaking the concrete structure.

It is readily observed that Vondran's clinker/fiber-intergrinding method(hereinafter the “Vondran method”) purports to achieve quick fiberwetting and uniform dispersion without the balling and clumping foundwhen adding the fiber components separately into concrete. The presentinventors, however, observe that the Vondran method teaches that “fiberprecursors” are combined with cement clinker particles into a ball millcement grinder, and that this process provides fibers that are“attenuated, roughened and abraded by the action of the clinkerparticles and the grinding elements on the fiber” (See U.S. Pat. No.5,298,071 at column 2, lines 58-66). This process purportedly results inimproved mechanical bonding between the cement and fibers.

In the present invention, however, the inventors seek to improve thepull-out resistance of fibers from concrete while avoiding the kinds ofmechanical or physical fiber attributes that might otherwise impede theability of the fiber to be introduced into, and uniformly dispersedwithin, the concrete mix. The present inventors believe that the clinkerintergrinding process of Vondran results in cement particles beingground into, and embedded in, the fiber surface. Moreover, thedeep-abrading action of the cement clinker may be undesirable becausethe fibers will tend to clump during humid conditions (e.g., storage,shipment) due to the hydrating cement particles. Furthermore, fibers cannot be interground with clinker at high volumes using ball millmachinery in an clinker-intergrinding process because the fibers wouldpotentially clog the classifier unit used in such mills for separatingground cement particles from the grinding operation. The presentinventors have also discovered that fibers interground in ball milloperations using clinker are severely abraded, and, in effect, areshredded to the point at which their mechanical integrity, for purposesof reinforcing concrete, is defeated. Such clinker-interground fibers,whether by abrasion and/or impact of clinker material, lose mechanicalresistance to pull-out from concrete (i.e., fracture toughness) becausethe fiber bodies and ends are shredded or devastated by theclinker/fiber intergrinding operation.

The terms “shredded” or “shredding” are used herein to refer to thetearing-apart of the fiber body into smaller elongated pieces. Theconcept of “shredding” as used herein is not equated herein with theconcept of “fibrillation”. The concept of fibrillation may be seen tooccur where a multifilament fiber, comprised of two or more strands orfibrils are adhered or bonded together, is separated into its componentstrands or fibrils. On the other hand, “shredding” is defined forpresent purposes as the act of breaking a fiber down (whethermonofilament or multifilament) into pieces smaller than the constituentstrands or fibrils.

In view of the disadvantages of the prior art as discussed above, thepresent inventors believe that a novel fiber for reinforcing matrixmaterials, and in particular hydratable cementitious materials such asconcrete and shotcrete, are needed. Also needed are novel methods formaking such fibers and for modifying such matrix materials.

SUMMARY OF THE INVENTION

In contrast to the above-described prior art fibers and methods formanufacturing reinforcing fibers, the present invention provides fiberswhich are micro-mechanically-deformed such that the fibers are flattenedand have surface deformations for improved contact with the matrixmaterial. Fibers of the invention are mechanically-flattened to providemacro-level deformations in terms of varying width and/or thicknessdimensions within fiber lengths, but are also “diastrophically” deformedto provide micro-level deformations (e.g., microscopic materialdisplacements) on the fiber surface. This is achieved while avoiding theobliterative clinker intergrinding process of the prior art.

The term “diastrophic,” as used herein is defined in Webster's Third NewInternational Dictionary (Merriam-Webster Unabridged Dictionary,Springfield, Mass.) as follows: an adjective “of, having reference to,or caused by diastrophism.” The term “diastrophism,” in turn, is definedin this Webster's dictionary as “the process of deformation thatproduces in earth's crust its continents and ocean basins, plateaus andmountains, folds of strata, and faults—.”

The present application, therefore, borrows geological terminology indescribing “micro-diastrophic” synthetic fibers which have a microscopicsurface “diastrophism”. After application of the flattening processes ofthe invention, a number of physical deformations or materialdisplacements caused or induced in the fibers can be seen under themicroscope to resemble geological morphologies or phenomena. Forexample, the microscopically viewed surfaces of the treated fibers haveirregularly and randomly elevated portions or ridges resembling islands,continents, plateaus, and mountains; and there can also be detectedequally random folds of strata, faults (or fissures), and other physicaldisplacements of fiber material. These microscopic deformationirregularities appear randomly on the surface of a given fiber, as wellas from fiber to fiber.

Thus, the term “micro-diastrophic” is appropriate for describing themicro-level deformations or physical displacements of exemplary fibersof the present invention. The term “micro-diastrophism” also appears todescribe the three-dimensional morphological changes achieved by thenovel methods of the invention. These morphological changes may beachieved by subjecting synthetic polymer material (preferably apolypropylene, polyethylene, or mixture thereof) to a compressive force.An exemplary compressive force may be achieved by using at least oneroller, and preferably opposed rollers to compress the fibers to induceirregular and random microscopic surface deformations that are describedherein as diastrophic; this process is very different from superficiallyembossing or crimping fibers. Alternatively, though less preferably, theeffect may be achieved by using a ball mill (without the use of cementclinker as taught by Vondran et al). The stress forces on the fibersshould be sufficient to flatten the fibers in a manner to increase andvary (within the length of the fiber) the fiber width dimension,thickness dimension, or both; and to cause or induce micro-diastrophismin the fiber surface as mentioned above. The micro-diastrophism in thefiber surface causes an increase in the total fiber surface area thatcan be placed into contact with the matrix material. Themicro-diastrophic surface deformities should be achieved withoutsubstantially shredding the elongated body or end portions of the fibers(e.g., without cement particles being embedded in, with attendantabrasion of, the fiber surface), although a small amount of fibrillationor shredding at the extreme fiber ends may be tolerated within thespirit of the present invention.

One advantage of the fibers of the invention is their ability to providestrong bonds with the matrix material (e.g., concrete). This is believedto arise from the fibers having a variable width and/or thicknessdimension(s), and enhanced bonding surface due to micro-diastrophism inthe fiber surface. These advantages are provided while avoiding asubstantial increase in fiber-to-fiber entanglement or clumping whichwould otherwise be expected to arise during or after mixing into thematrix material. Another advantage of the invention is that, in theabsence of using the prior art clinker-intergrinding method, the fibersand methods of the present invention are substantially free of embeddedcement/clinker particles and the abrasive and obliterative shreddingcaused by the prior art clinker-intergrinding operation.

Thus, the present invention provides high performance fibers and methodsfor reinforcing matrix materials against cracks without entailing theproblems of prior art reinforcing fibers. Exemplary fibers of theinvention comprise a plurality of mechanically-flattened fibers havinggenerally elongate bodies, opposed body ends defining a fiber length,said fiber bodies have varied width and/or thickness dimensions andhaving micro-diastrophic surface deformities. Matrix materials andstructures comprising such fibers are also disclosed and claimed. Anexemplary method of the present invention for manufacturing fiberscomprises providing a plurality of synthetic polymer fibers, andmechanically flattening these fibers to the extent that the fibers,after said mechanical flattening, have a varied width and/or thicknessdimension and micro-diastrophism. Further advantages and features of theinvention are further described in detail hereinafter.

BRIEF DESCRIPTION OF EXEMPLARY DRAWINGS

An appreciation of the advantages and benefits of the invention may bemore readily apprehended by considering the following writtendescription of preferred embodiments in conjunction with theaccompanying drawings, wherein

FIG. 1 is a before-and-after diagram of a single polymer fiber untreated(10) and an exemplary single polymer fiber treated by a preferred methodof the present invention (12);

FIG. 2 is a before-and-after diagram of a multipolymer blend fiberuntreated (20) and an exemplary multipolymer fiber treated by apreferred method of the present invention (22);

FIG. 3 is micrograph of a side view of a single polymer fiber(untreated);

FIG. 4 is a micrograph of a side view of a multipolymer blend fibersurface (untreated);

FIG. 5 is a micrograph at higher magnification of a multipolymer blendfiber surface (untreated) of FIG. 4;

FIG. 6 is a micrograph of the surface of a single polymer fiber afterintergrinding with cement clinker in a ball mill (prior art method);

FIG. 7 is a micrograph of a shredded multipolymer blend fiber afterintergrinding with cement clinker in a ball mill (prior art method);

FIG. 8 is micrograph of a shredded multipolymer blend fiber surfaceembedded with cement particles after intergrinding with clinker in aball mill (prior art method);

FIG. 9 is a micrograph of exemplary micro-diastrophic surfacedeformations of a single polymer fiber treated by the method of thepresent invention;

FIG. 10 is a micrograph of exemplary micro-diastrophic surfacedeformations of a multipolymer blend fiber treated by the method of thepresent invention;

FIG. 11 is a micrograph of the edge view of an exemplary single polymerfiber (shown adjacent to open cells of adhesive mounting substrate usedfor handling fiber during viewing) treated by the method of the presentinvention;

FIG. 12 is a micrograph of exemplary micro-diastrophic deformations onsurface of a multipolymer blend fiber treated by the method of thepresent invention;

FIG. 13 is a micrograph of exemplary micro-diastrophic deformations onsurface of a multipolymer blend fiber treated by the method of thepresent invention (tiny whitish specks are believed to be fiber polymer“dust”); and

FIG. 14 is a micrograph along an edge of an exemplary multipolymer blendfiber treated by the method of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present inventors believe that the fibers of the present inventionmay be used in a variety of compositions and materials and structuresmade from these. The term “matrix materials” therefore is intended toinclude a broad range of materials that can be reinforced by the fibers.These include adhesives, asphalt, composite materials (e.g., resins),plastics, elastomers such as rubber, etc. and structures made therefrom.Other matrix materials include hydratable cementitious compositions suchas ready-mix concrete, precast concrete, masonry mortar and concrete,shotcrete, bituminous concrete, gypsum-based compositions (such ascompositions for wallboard), gypsum- and/or Portland cement-basedfireproofing compositions (for boards and spray-application), and otherhydratable cementitious compositions, whether in dry or wet mix form.

A primary emphasis is placed upon the reinforcement of structuralconcrete (e.g., shotcrete) however, since concrete (whether poured,cast, or sprayed) is an extremely brittle material which presentschallenges in terms of providing reinforcing fibers which (1) can besuccessfully introduced into and mixed in this matrix material and (2)can provide crack-bridging bonding strength in the resultant concretestructure.

Prior to a detailed discussion of the various aforementioned drawingsand further exemplary embodiments of the invention, a brief discussionof definitions will be helpful to facilitating a deeper understanding ofadvantages and benefits of the invention. As the fibers of the inventionare envisioned for use in the paste portion of a cement or concrete(terms which are sometimes used interchangeably herein), it is helpfulto discuss preliminarily the definitions of “cement” and “concrete.”

The terms “paste,” “mortar,” and “concrete” are terms of art: pastes aremixtures composed of a hydratable cementitious binder (usually, but notexclusively, Portland cement, masonry cement, or mortar cement, and mayalso include limestone, hydrated lime, fly ash, blast furnace slag,pozzolans, and silica fume or other materials commonly included in suchcements) and water; mortars are pastes additionally including fineaggregate (e.g., sand); and concretes are mortars additionally includingcoarse aggregate (e.g., gravel, stones). “Cementitious” compositions ofthe invention thus refer and include all of the foregoing. For example,a cementitious composition may be formed by mixing required amounts ofcertain materials, e.g., hydratable cementitious binder, water, and fineand/or coarse aggregate, as may be desired, with fibers as describedherein.

The fibers of the present invention are preferably comprised of at leastone synthetic polymer (e.g., a polyolefin) and more preferably a“multipolymer” blend which comprises two or more polymers (e.g.,polypropylene and polyethylene; polypropylene and polystyrene). Whileexemplary fibers of the invention may comprise a single polymer such aspolypropylene, the more preferred embodiments may comprise monofilamentswhich have two or more polymers, such as polypropylene and polyethylene,or other polymers having different moduli of elasticity. A suitablemultipolymer blend fiber is disclosed, for example, in World PatentAppln. No. WO 99/46214 of J. F. Trottier et al., which is incorporatedherein by reference. Exemplary fiber material is also commerciallyavailable from East Coast Rope Ltd., of Syndey, Nova Scotia, Canada,under the tradename “POLYSTEEL”. Fibers which can be used in concrete,for example, includes any inorganic or organic polymer fiber which hasthe requisite alkaline resistance, strength, and stability for use inreinforcing hydratable cementitious structures. Synthetic polymermaterials are preferred. Exemplary fibers of the invention are syntheticmaterials such as polyolefins, nylon, polyester, cellulose, rayons,acrylics, polyvinyl alcohol, or mixture thereof. However, polyolefinssuch as polypropylene and polyethylene are preferred. Polyolefins may beused in monofilament, multifilament, collated fibrillated, ribbon form,or have shapes or various sizes, dimensions, and arrays. Fibers may becoated, using the materials taught in U.S. Pat. No. 5,399,195 of Hansen(known wetting agents) or in U.S. Pat. No. 5,753,368 of Berke et al.(concrete bonding strength enhancement coatings). It is suspected by thepresent inventors that the use of different polymer molecular weights(e.g., a broad range) may be advantageous in helping to obtain variedwidth and/or thickness dimensions and a highly irregular surfacemorphology.

Preferred fibers are provided in “monofilament” form. The term“monofilament” refers to the shape of the treated fiber which isprovided (literally) as “one filament” (ie. a unified filament). Theterm “monofilament” as used herein does not preclude the possibilitythat the singular filament may, when subjected to agitating forceswithin a concrete mix (e.g., one having fine and/or coarse aggregates),break down further into smaller filaments or strands when subjected tothe agitation, for example, in a concrete mix due to the comminutingaction of aggregates (e.g., sand, stones, or gravel). The term“monofilament” is used in contradistinction from the term“multifilament” which refers to a bunch of fibers that are intertwinedtogether or otherwise bundled together such that they have a pluralityof separate strands. (To large extent, a fiber can be defined as eithermonofilament or multifilament depending upon whether one is able tovisually discern the separate fibrils at a certain point in time). Inany event, the fibers and methods of the present invention arecontemplated to include, and to be applicable to, both monofilament andmultifilament fibers. The methods of the present invention are alsobelieved to be suitable for use with fiber precursors (e.g.,fibrillatable sheets), fibrillated fibers, and fibers assembled intounits such as intertwined fiber bundles, rope, or braided cords whichcan be subjected to mechanical flattening and micro-surfacedeformations.

A preferred embodiment of the invention pertains to “multipolymer”fibers. It is believed by the present inventors that such fibers (havingtwo or more different polymers, such as a mixture of polypropylene andpolyethylene or a mixture of polypropylene and polystyrene, for example)provide better pull-out resistance from hydratable cementitious matrixmaterials (e.g., ready mix concrete). It is surmised that the differentmoduli of the polymers increases the chance of obtaining the variablewidth or thickness dimensions and surface deformations desired. Also,the use of multipolymer fibers better demonstrate the superiority of themethods of the present invention when compared to the prior artclinker-intergrinding process (taught by Vondran), because thedestruction and shredding of multipolymer fibers under the prior artVondran method is highly discernible both to the naked eye and undermicroscopic magnification.

Generally, the fibers of the invention may be cut into desired lengthsbefore or after mechanical flattening. Fibers for reinforcing matrixmaterials preferably (after cutting) have average lengths of about 5-75mm; average widths of 0.5-8.0 mm.; and average thicknesses of 0.005-3.0mm. It is possible to exceed these preferred limits without strayingfrom the spirit of the present invention. The length, width, andthickness dimensions may depend on the nature of the fiber material anduse contemplated (e.g., polyolefin, carbon, polyamide, etc.) and thematrix material contemplated for reinforcement (e.g., concrete, asphalt,plastic, glass, composite material, rubber, latex, adhesive, etc.). Theunique and novel morphologies of the fibers of the present invention areintended to be used over a range of fiber and matrix materials, althoughthe greatest challenge and the predominant purpose of the presentinvention is to provide fibers having at least one synthetic polymer,and preferably at least two (“multipolymer”) polymers blended together,for reinforcing hydratable cementitious matrix materials such asconcrete.

Exemplary fibers of the present invention may be made by subjecting aplurality of fibers, or one or more fiber precursors (e.g., a polymersheet cut or scored to provide “fibrillated” fibers, a bundle ofmonofilaments, continuous monofilament(s) or multifilament strands thatis/are subsequently cut to the desired length, etc.) to deform the widthand/or thickness dimensions, preferably to provide a macro-level keyingeffect through width and/or thickness dimensions that vary along thefiber length by at least 5%, more preferably by at least 10%.

FIG. 1 is an illustration of an untreated polypropylene fiber 10 whenviewed under microscope. The untreated fiber 10 has an essentiallyuniform width dimension (w) along its entire length. When a plurality ofsuch fibers 10 is introduced randomly between opposed rollers andflattened a few times by reintroducing the fibers randomly between therollers, the fibers become substantially flattened 12, particularly atthe opposed ends 14, where the end width (w′) can be seen to besubstantially greater than some of the narrow body width sections (e.g.,w″). Moreover, while the untreated fiber 10 will be seen undermicroscope to be generally translucent, the variably flattened fiber 12will be seen to be less translucent due to internal and superficialstresses (generally indicated by the lines drawn as at 16) which can bemore readily appreciated when viewed at higher magnification.

FIG. 2 is an illustration of an untreated multipolymer fiber 20comprising, for example, a blend of polypropylene and polyethylene.After mechanical flattening, the flattened fiber 22 demonstrated a widthincrease at the fibers ends 23 and less translucence which indicatedinternal and superficial stresses (26).

FIG. 3 is a micrograph taken at 33× magnification of an untreated singlepolymer (polypropylene) fiber. The uniformity of width dimensions caneasily be viewed.

FIG. 4 is a micrograph taken at 45× magnification of an untreatedmultipolymer blend (polypropylene/polyethylene) fiber. This alsodemonstrates a fairly uniform width dimension. At this magnification,slight striations in the surface can be detected, and these features arebelieved to be due to the effect of the extrusion die used to form thefiber. FIG. 5 is a micrograph taken at higher magnification (4500×). Thestriations can now be seen a small but relatively uniformly shapedgrooves between relatively smooth polyblend (polypropylene/polyethylene)fiber. This also demonstrates a fairly uniform width dimension. At thismagnification, slight striations in the surface can be detected, andthese features are believed to be due to the effect of the extrusion dieused to form the fiber. FIG. 5 is a micrograph taken at highermagnification (4500×). The striations can now be seen as small butrelatively uniformly shaped grooves between relatively smooth polymersurfaces of the fiber. A large groove or channel is seen runningdiagonally upwards from left corner to right corner of the micrograph,and this is believed to be due to polymer separation in the multipolymerblend.

FIG. 6 is a micrograph taken at 50× magnification of a polypropylenefiber subjected to intergrinding with cement clinker in a smalllaboratory-scale steel ball mill. This is the effect of the prior artVondran process. The surface is embedded with cement particles (largewhitish areas.) The width dimensions are not substantially varied by theball mill clinker intergrinding. In any event, the present inventorsattempted to simulate the ball mill process without the use of a ballmill as actually used in grinding cement clinker, because they do notbelieve that any fibers would actually be left if an actual ball millfor clinker intergrinding (i.e. actual cement manufacture) were used astaught by Vondran.

FIG. 7 is a micrograph at 50× enlargement of a multipolymer fiber(polypropylene/polyethylene) that was subjected to the prior art Vondranclinker intergrinding process in a ball mill. The fiber was shredded andabraded by the action of the clinker material during intergrinding. (Theedge of a piece of tape can be seen in the micrograph; this was used tohandle the fiber during viewing). The integrity of this fiber isobliterated and rendered essentially useless for purposes of reinforcingcementitious materials. This shredded fiber would likely causefiber-to-fiber entanglement and mixing difficulties.

FIG. 8 is a micrograph at 900× magnification of a multipolymer fibersubjected to clinker-intergrinding. The embedded cement clinkerparticles can now be more readily seen embedded into the fiber surface.The nature and severity of the shredding can be more readilyappreciated, because extremely tiny microfilaments (many less than 5 um)can be seen to have separated completely from adjoining fiber material,and this is believe to be an impediment to the task of reinforcingconcrete.

FIG. 9 is a micrograph at 900× magnification of the surface of a singlepolymer (e.g., polypropylene) fiber flattened in accordance with themethods of the present invention. A plurality of fibers were flattened anumber of times by random introduction through opposed rollers. Thefibers were compressed such that they had variable width and/orthickness dimension(s) (as will be shown later), but most significantlythe fiber surfaces had micro-diastrophic features. Readily seen areelevated or raised portions, ridges, mountain-like “terrain,” as well asdepressions, folded strata (there is a round-shaped folding seen nearthe upper left corner of the micrograph), as well as irregular andrandom fissures or breaks in the material. This microscopic diastrophismcan be seen as an increased surface area. Such micro-diastrophic changein the fibers cannot be achieved merely by placing fibers betweenembossed rollers to cut or roughen the surface, but can only be achievedby exerting sufficient great pressures on the fibers to achieveirregular and random displacement or dislodgment of masses of the fiberpolymer material.

It is with reference to micrographs such as provided in FIG. 9 that onecan sense the metaphoric or poetic appropriateness of the definition of“diastrophism” as provided in Webster's Third New InternationalDictionary: “the process of deformation that produces in earth's crustits continents and ocean basins, plateaus and mountains, folds ofstrata, and faults—.” For example, the reference to “ocean basins” seemsespecially appropriate for the fiber surface morphology shown in FIG. 9,because the elevations and depressions of physical fiber material asshown are fluid-like in the manner of an ocean floor, or they otherwisesuggest or resemble glacial erosions or shifting.

FIG. 10 is a micrograph at 900× magnification of a multipolymer(polypropylene/polyethylene) blend fiber that was treated in accordancewith the flattening process of the invention. The micro-diastrophismseen is also random, showing elevated peaks and depressions of fibermaterial. Irregular elevated ridges can be seen to span over depressionsand/or fissures of discontinuous micro-fractures in the polymericmaterial. The polymer material can be said to be “smeared” andphysically displaced by the flattening process of the invention in anirregular, non uniform manner.

FIG. 11 is a micrograph taken at 40× magnification of an edge view of asingle polymer (polypropylene) fiber (shown adjacent to open cells ofadhesive used for handling the fiber) that was flattened in accordancewith the method of the present invention. The thickness dimension caneasily be seen to vary along the fiber length, and the micro-diastrophicsurface deformations along the edge are suggested by light reflectingoff the surface edge.

FIG. 12 is a micrograph across the width of a multipolymer blend(polypropylene/polyethylene) fiber treated by the method of the presentinvention. The width varied from 1.57 to 1.73 mm at one point, while themicro-diastrophic deformations of the surface could also be appreciated.

FIG. 13 is a micrograph at 2,500×× magnification of a multipolymer blendfiber (polypropylene/polyethylene) treated by the flattening process ofthe present invention. The whitish specks (about 5 um or less) are bitsof polymer from the fiber which are not believed to defeat the abilityof the fiber to bond with matrix materials such as concrete, asphalt, orother materials. The micro-diastrophism can be seen to includediscontinuous stress-fractures between and among areas of continuities(plateaus or ridges) of varying elevations which are shown withdifferent shading in the micrograph of FIG. 13.

FIG. 14 is a micrograph at 190× magnification of an edge of amultipolymer blend fiber flattened by the process of the presentinvention. The thickness of the fiber varied at points, from 173 um, to161 um at another point, and to 152 um at yet another point. (A tapesubstrate is depicted at the left of the picture; this was used forhandling the fiber). Towards the right of the micrograph, there areelevated portions of the fiber surface that are visibly evident in thedistance. The surprising micro-diastrophism induced in the fiber surface(or face on the edge-to-edge side) can be especially appreciated by themicrograph of FIG. 14. Particularly remarkable is that the flatteningstress force, which is applied against the fiber, induces both anoncontinuous micro-fracture (i.e., a fissure of finite length) as wellas elevated ridges in the displaced polymeric fiber material.

Exemplary methods of the invention provide fibers having varying widthsand/or thickness dimensions and micro-diastrophism in the fiber surface.A preferred method comprises exerting a compressive force on fibers,preferably by using the compressive action of at least one roller, andmore preferably by cooperative action of opposing rollers, to compressfiber material to the point at which the fiber materials is physicallydisplaced first on a macro-level (affecting the general shape or profileof the fiber as evident to the unaided human eye) and, second, on amicro-level whereby the microscopic fiber surface morphology is alteredto include irregular and random elevated portions and “fissures” (ordiscontinuous stress-fractures) in the polymer material.

Preferably, at least one roller or series of rollers is/are rotated upona stationary surface or conveying surface upon which the fiber materialor fiber precursor is situated. The fiber material may be supplied inthe form of continuous fibers, which may be cut after flattening, orpre-cut fiber lengths; or they may be supplied in the form offibrillatable or scored sheets or braided or interwoven sheets, ropes,cords, etc. Thus, an exemplary method comprises introducing a pluralityof cut fibers (e.g., average length of 5-75 mm) randomly between opposedrollers, such that fibers can be pressed against each other as they passbetween opposed rollers. More preferably, the fibers are subjected tosuch flattening at least two or more times between the same rollers orother rollers. For example, fibers may be subjected to a series ofopposed rollers, each roller having increasing textured surfaces forachieving microscopically sized displacement of polymer material(micro-diastrophism) on the fiber surface.

Rollers are preferably steel. As polymer synthetic fibers are generallyprovided having equivalent diameters (or thicknesses) of average 0.5-1.0mm, the steel rollers may be set apart at a distance somewhat less thanthis (say about 0.01-0.3 mm), depending upon the nature of the fibermaterial, ambient temperature, and other processing conditions. Anexemplary method of the invention, therefore, comprises feeding aplurality of fibers or fiber precursors, either in an uncut or cut state(e.g., average 5-75 mm), between the opposed steel rollers to providemacro-level deformation as well as micro-diastrophic deformation on thefiber surfaces.

In preferred processes, the varied widths and/or thicknesses of thefibers can be achieved by varying the distance between opposed rollers(or between roller and other contact surface between which fibers arepassed); by using textured rollers whereby the texture is operative toprovide a varied compressive force sufficient to achieve random physicaldeformation in the fiber shape; and/or by subjecting two or moreoverlapping fibers randomly between opposed rollers. The presentinventors also believe that macro-level and micro-level deformations maybe obtained in the fibers by hitting the fibers randomly, or conveyingfibers in a random fashion, under hammers or other objects capable ofcompressing certain portions of the individual fibers with sufficientstress forces.

The inventors have also discovered other surprising ways of achievingthe desired deformation morphology and micro-stress-fracturing in thefibers using rollers. One way is to alter the surface of at least oneroller, such as by roughening the surface by using it to crush brittlematerials, such as stone, gravel, clinker, and the like; and thensubsequently introducing fibers between rotating rollers wherein atleast one, and preferably two or more, of the rollers have the roughenedsurface. Such surface-roughened or “textured” roller surfaces shouldpreferably have a random structure or pattern, although it is possibleto have the rollers textured with a irregular or non-uniform patterns(e.g., dimples, protrusions, grid patterns, line patterns, raisedportions, indentations, grooves, or a combination thereof) against whichor between which (as in opposed rollers) the fibers may be (preferablyrandomly) compressed, deformed and/or fractured.

In still further exemplary processes of the invention, the fibers may beintroduced to the deforming action of rollers more than once, or,alternatively, may be subjected to a succession of rollers (preferablywith each set of rollers inducing a greater degree of deformity and/ormicro-fracturing compression force).

Another process of the invention comprises conveying a continuous strandor strands of fibers between compressive forcemicro-diastrophic-inducing means, such as rollers or hammers, wherebythe fibers are flattened along the length of the fiber, and then cuttingthe fiber strand or strands such that individual fibers are producedhaving varied widths and/or thicknesses along the individual fiberlength. Less preferably, the flattening of the fibers can beaccomplished by using steel balls in a rotating mill or containerwithout clinker or cement particles being interground, and thus withoutsubsequently having embedded cement particles on the fiber surfaces;this is less preferable, as the ability to obtain variable width and/orthickness dimensions in the individual fibers is much more difficult tocontrol.

The present invention also includes matrix materials, such as asphalt orcementitious compositions, incorporating the exemplary fibers describedherein, such as concrete compositions comprising a binder, a fineaggregate and/or coarse aggregate (and fibers). Accordingly, exemplarycompositions include the fibers of the invention in a matrix materialsuch as concrete, ready-mix concrete, masonry concrete, shotcrete,bituminous concrete, and structures made from these compositions,including foundations, walls, retaining wall segments, pipes, slabs,decks, surface coatings, and other building and civil engineeringstructures. Asphalt compositions containing fibers of the invention, aswell as structures made from such compositions, such as roads, surfaces,decks, walks, patch materials, and the like, are also within the presentinvention. The compositions may be supplied in either wet or dry form.These would also include dry and wet compositions comprising shotcreteor other spray-applicable materials, such as gypsum and/or Portlandcement-based fireproofing, and their coatings and coated structures.

The invention also pertains to packaged fibers wherein a plurality ofthe exemplary fibers described herein are packaged in average fiberlengths of 5-75 mm within a container, such as a bag, peripheral bundlewrapping, capsule, box, carton, adhesive, wetting agent, bonding agent,or other packaging means that is operative to hold the fibers together,whereby their total outer surface area is diminished to facilitateintroduction of the fibers into the cement or concrete mix, and wherebytheir uniform dispersion within the matrix material is facilitated. Whenintroduced into the matrix material (and subjected to agitation, water,heat, or other initiating condition therein), the packaging material canbe made to dissolve, abrade, rupture, or otherwise disrupt, therebyreleasing the fibers into the mix and allowing them to present a largertotal surface area to become mechanically engaged with the matrixmaterial.

In the concrete arts, a package suitable for accomplishing this isavailable from Grace Construction Products, Cambridge, Mass., under theregistered tradename CONCRETE-READY BAG®. This packaging comprises anon-water-soluble paper. Other packaging, which may be water-soluble,such as polyvinyl alcohol, may also be employed for purposes of thepresent invention.

Fibers may also be bundled by using an abradable or dissolvableperimeter wrap as taught in U.S. Pat. Nos. 5,807,458 and 5,897,928 bothowned by 3M of Minnesota. Alternatively, fibers may be releasablyadhered together using a water-soluble adhesive or wax or otherreleasable inter-fiber bonding agent, such that the individual fibersmay become separated and dispersed uniformly during agitation of thecement mix.

It is preferable to subject the fibers, whether in cut or uncut state,or fiber precursors (e.g., fibrillatable or scored sheets) tocompressive stress forces in a dry state (although known wetting agentsor surface-active agents can be used to decrease static charge) andpreferably at or below ambient (room) temperature before the fibers arecoated or packaged. Treatment of the fibers using the techniques of thepresent invention is best accomplished when the fiber material is near,at, or below room temperature to induce micro-diastrophism in the fibermaterial, (observable under microscope—e.g., at 5×-4000× or moremagnification). In other words, at the risk of belaboring the point, ifthe fiber material is subjected to compressive stress when the fibersare warm (e.g., after extrusion), then the fiber material can beresiliently compressible rather than brittle and may not be caused todeform by operation of the rollers or other flattening means. Rather,after extrusion, the fibers should be allowed to cool (or otherwiseshould be chilled) before being subjected to compressive stressessufficient to induce macro-level width or thickness variability as wellas micro-diastrophism in the fiber surface structure.

In one exemplary method of the invention, fiber material is continuouslyfed (in continuous strands, although cut strands can be used) betweensteel rollers, whole surface is textured by prior crushing of stones andgravel, to cause flattening and varying of the width and/or thicknessdimensions and further to cause the fibers have micro-diastrophism intheir surfaces. The fibers may optionally be coated (such as with aconventional wetting agent, anti-static coating material, bonding agentor other coatings as may described above), before or after flattening;then they can optionally be bundled together such as by a peripheralwrap and/or interfiber bonding materials, and then optionally cut (ifneeded) into shorter average fiber lengths (with the average fiberlength, for use with cementitious materials, preferably in the averagerange of 5-75 mm).

An exemplary method of the invention for making the aforementionedfibers comprises subjecting a plurality of synthetic polymer fibers toflattening forces so as to create varying width and/or thicknessdimensions and to diastrophically deform the fiber surface, withoutsubstantially embedding concrete particles into such surfaces andwithout substantially shredding the opposing ends and elongate bodies ofthe fibers.

An exemplary method of the invention for modifying a matrix material,such as a cementitious composition, comprises introducing into thematrix material the above-described exemplary fibers of the invention.The fibers are preferably contained within a packaging means operativeto minimize initial total surface area of the fibers and also operative,upon agitation of the material mix, to dissolve or abrade or disrupt thepackaging and release the fibers into the matrix material mix.

Thus, an exemplary method for reinforcing hydratable cementitiousmaterials comprises: adding to a cement, mortar, cement mix, or concretemix (dry or wet), in an amount of 0.05-15% weight based on percentagevolume (of total dry solids) the above-described exemplary fibers of theinvention. The composition is then mixed to obtain a concrete, mortar,or paste mix in which the individual fibers are released from thepackaging and homogeneously distributed within the mix. The mix is thencast into a configuration or structure. More preferably, the additionamount of fibers is 0.1-5 vol. %, and more preferably 0.5-2 vol. %,based on concrete. The term “configuration” means and refers to afoundation, a rectangular shaped slab, a wall, a block, a segment of aretaining wall, a pipe, or portion of a civil engineering structure,bridge deck, tunnel, or the like.

A preferred embodiment of the present invention comprises a plurality offibers having the exemplary macro-level and micro-level deformationsdescribed above, which fibers are bundled (either physically or bywetting agents) and/or packages (such as in a disruptable or dissolvablecontainer) to minimize initial total surface area of the fibers (tofacilitate introduction into and dispersal of the fibers within thematrix material). Upon agitation of the material mix or by operation ofthe water in the mix, bundling and packaging becomes either abraded ordissolved or otherwise disrupted, thereby releasing fibers into the mixand allowing the micro-diastrophically deformed fiber surface area tocontact the matrix material (e.g., concrete, shotcrete mix, gypsumwallboard material, sprayable fireproofing, etc.).

For application into a concrete matrix material, as one example, theplurality of fibers may be separately bundled and/or packaged togetherwithin bags or containers, such as Grace Concrete Ready-Bag® packagingas previously described.

EXAMPLE 1 Comparative Physical Data

The present inventors do not believe that polymer fibers subjected tothe Vondran method, employing clinker in an actual industry cementmanufacturing ball mill, would have any residual integrity, but would beobliterated after intergrinding. Thus, they attempted to reproduce intheir laboratory an intergrinding process that would leave a fiber withsome semblance of its form, for comparative purposes. The ball used hada one cubic foot capacity and was loaded with about 22700 grams weightof steel balls having diameters between 12 and 17 mm on average andabout 2400 grams total weight of cement clinker having diameters between0.01 and 0.1 mm. About 100 grams of fibers was loaded into the mill,which was then operated at 45 revolutions per minute for a period of 30minutes.

Polypropylene fibers available from 3M and multipolymer (e.g.,polypropylene/polyethylene) blend fibers available from GraceConstruction Products were used. Such multipolymer fibers are generallycommercially available. The micrographs of these fibers (untreated) wereprovided in FIGS. 3 and 4, respectively.

If the ball mill operation is run for a period of time that is less thanwhat is required for grinding clinker into cement, the results may betypified by FIG. 4a, which shows the ends of the interground fibersubstantially shredded apart. The inventors even attempted to repeat theball mill intergrinding operation using cement particles alone withoutclinker, but the fibers were also severely damaged and containedembedded cement particles. Micrographs of fibers, when treated by thecement clinker intergrinding ball mill method, were provided in FIGS. 6and 8 (single polymer) and FIG. 7 (multipolymer).

As seen in the micrographs of FIGS. 7 and 8, when fibers wereinterground with clinker in a ball mill, the fiber surfaces are abradedand embedded with cement clinker. As shown in FIG. 8, in particular, thefiber is shredded to the point at which the fiber integrity isessentially destroyed.

EXAMPLE 2

Micrographs of fibers treated by exemplary flattening methods of thepresent invention are provided in FIGS. 9-14. The surfaces containmicro-diastrophic material displacements and contain no embedded clinkerand have no substantial shredding (e.g., complete separation of fibrilsor strands that destroys the physical integrity of the fiber). Thefibers were treated by introducing a plurality of fibers randomly, oftenoverlapping one another, between opposed steel cylinders which werespaced apart a distance that was less than the fiber thickness, suchthat physical flattening occurred in the general shape of the fiber andmicro-diastrophism occurred on the surface of the fibers. It is believedthat the distance between opposed rollers was about 10%-50% the averagediameter dimension of the fibers. The macro-level and micro-leveldeformations perceived were especially pronounced when a multipolymerblend fiber (Grace Structural Fiber) was subjected to the method of thepresent invention, and passed between the rollers at least two or threetimes.

It is surmised by the inventors that the various surface portions offibers treated by the flattening method of the present invention willdemonstrate fractal geometry in the sense that the irregular and randommicro-level-deformities (micro-diastrophism) will appear at increasinglyhigher magnifications of the surface.

The present invention is not to be limited by the foregoing exampleswhich are provided for illustrative purposes only.

It is claimed:
 1. A method for making fibers for reinforcing matrixmaterials, comprising: providing a plurality of fibers comprising atleast one polymer; mechanically flattening and cutting said fibersthereby to obtain mechanically-flattened fibers having generallyelongate bodies, said bodies having an average length of 5-75 mm., anaverage width of 0.5-8.0 mm., and an average thickness of 0.005-3.0 mm.;the average fiber width of said mechanically-flattened fibers exceedingthe average fiber thickness; said fiber bodies having irregular andrandom displacements of polymer material on the fiber surface, saidfiber surface displacements comprising microscopic noncontinuous stressfractures and microscopic elevated ridges.
 2. The method of claim 1wherein said mechanical flattening of said fibers is accomplished usingat least one roller.
 3. The method of claim 1 wherein said mechanicalflattening of said fibers is accomplished by at least two rollers. 4.The method of claim 1 wherein said fibers are flattened using balls in arotating mill without cement clinker.
 5. The method of claim 1 whereinsaid fibers comprise at least one synthetic polymer.
 6. The method ofclaim 1 wherein said fibers comprise at least two different polymersblended together.
 7. The method of claim 1 wherein said mechanicalflattening is accomplished by introducing continuous fibers betweenopposed rollers, and varying the compressive force of exerted on thefibers by the rollers, whereby varying width and/or thickness dimensionsare provided.
 8. The method of claim 1 wherein said fibers are cutbefore or after mechanical flattening.
 9. The method of claim 1 whereinsaid fibers are mechanically flattened at ambient temperature.
 10. Themethod of claim 1 wherein said variable width and/or thicknessdimensions are provided by partially overlapping fibers as they passbetween opposed rollers.
 11. The method of claim 1 wherein at least oneroller is used for mechanically flattening said fibers, said at leastone roller having a surface roughened by stones or gravel.
 12. Themethod of claim 1 wherein said fibers comprise a material selected frompolyolefins, nylon, polyester, cellulose, rayons, acrylics, polyvinylalcohol, or mixture thereof.
 13. The method of claim 12 wherein saidfibers comprise polypropylene.
 14. The method of claim 13 wherein saidfibers further comprise polyethylene or polystyrene.
 15. The method ofclaim 1 wherein said fibers are mechanically flattened in monofilamentform.
 16. The method of claim 1 wherein said fibers are mechanicallyflattened in multifilament form wherein said fibers a e twisted togetherto form the multifilament.
 17. The method of claim 15 wherein saidmonofilament fibers comprise a multipolymer blend.
 18. The method ofclaim 16 wherein said multifilament fibers comprise a multipolymerblend.
 19. The method of claim 1 wherein said fibers are mechanicallyflattened as intertwined fiber bundles, rope, or braided cords.
 20. Themethod of claim 1 wherein said mechanically flattened fibers comprise atleast two polymers having different moduli of elasticity.